This invention relates to solid-state color imaging devices and, more particularly, to a passive color coding filter for use with a charge-coupled imaging device.
As is well known, transmission of a color representation of a scene requires three independent video signals. These signals must be registered to produce an acceptable reconstructed image and a color television camera using only a single imaging device assures this registration. A camera having only one imaging device is, of course, also preferred over multiple imaging devices for obvious economic reasons.
One common format of the three independent video output signals includes two line-sequential chrominance (color difference) signals and a continuous luminance signal; that is, in each alternating horizontal scan line a different color difference signal is produced while all scan lines produce the luminance signal. Furthermore, it is desirable to operate with the conventional 2:1 line interlace in the vertical direction. While these characteristics can be provided by sampling each of a number of points in an imaging area and then electrically processing or matrixing the resulting outputs, it is by far more efficient to use optical filtering which permits the imaging device to produce the desired electrical signals directly, without matrixing.
When a single imaging device is used the color information is generated by a color coding filter which is placed between the scene and the device. While color coding filters having three-color stripe sets have been used extensively with electron beam scanning cameras, a new solid-state imaging structure, referred to herein as a charge-coupled-device or CCD, has been developed and the prior striped filter arrangements are not necessarily compatible with the CCD operation.
The charge-coupled-device concept is now well known, having been described extensively in the technical literature and prior patents. In particular, U.S. Pat. No. 3,801,884 issued Apr. 2, 1974 to C. H. Sequin, describes various charge transfer arrangements in area-imaging charge-coupled-devices. FIG. 5 of that patent illustrates a three-phase-transfer scheme which provides a 2:1 line interlace scanning format. In essence, two spatially overlapping cell patterns are formed, and one pattern of resolution cells produces a signal in one field and the other pattern of resolution cells produces a signal in the second field.
Since the color coding filters designed for the beam scanning devices are not generally suitable for the area-imaging charge-coupled-devices, and are particularly inappropriate for use with the three-phase transfer device providing the 2:1 interlace, it is an object of the present invention to provide a passive filter suitable for color coding the light impinging upon an area-imaging charge-coupled-device having a line interlace scanning format. In particular, it is an object of the present invention to provide a color coding filter suitable for use with a three-phase area-imaging charge-coupled-device having a 2:1 line interlace scan.
It is a further object of the present invention to provide line sequential color difference signals and a continuous luminance signal directly from the output of an area-imaging charge-coupled device without the need for matrixing or signal processing.